1. Field of the Invention
The present invention relates to a lamb wave device which excites a lamb wave in a piezoelectric thin film.
2. Description of the Background Art
Japanese Patent Application Laid-Open No. 2007-228319 discloses a bulk acoustic wave device that excites thickness longitudinal vibration or thickness-shear vibration in a piezoelectric thin film obtained by removal processing on a piezoelectric substrate. In this bulk acoustic wave device, since a frequency is inversely proportional to a film thickness of the piezoelectric thin film, in order to make the frequency high, it is necessary to reduce the film thickness of the piezoelectric thin film. For example, in order to set the frequency to several GHz, it is necessary to set the film thickness of the piezoelectric thin film to approximately several μm depending upon a piezoelectric material constituting the piezoelectric thin film.
However, when the film thickness of the piezoelectric thin film becomes as thin as several a problem arises where variations in film thickness that occur due to variations in processing cause large variations in frequency.
On the other hand, International Publication No. 2007-046236 discloses a lamb wave device that excites a lamb wave in a piezoelectric thin film. In this lamb wave device, an influence exerted by variations in film thickness upon variations in resonant frequency is smaller than in the case of the foregoing bulk acoustic wave device.